Notes about the data
1. Negative/zero issues and journeys
There are instances where negative ticket issues are reported. This happens when wholesale sellers of tickets return unsold stock and the returned stock exceeds the number of sales. A prime example is in April 2010 which coincides with the introduction of MyZone ticketing. Resellers returned unsold TravelPass Weekly tickets over a number of months but all returned tickets were assigned to April 2010, resulting in a negative number of journeys for that month.
For some longer term ticket types discontinued after the introduction of MyZone ticketing (e.g. TravelPass Weekly, Quarterly and Yearly) there are instances of monthly data where there are zero ticket issues that still have journeys attributed in the same month. This is due to journeys being attributed to tickets of this type which were sold in earlier months before being discontinued.